This invention relates to a clamp for connecting two electrical conductors, particularly in the form of cables, the clamp being particularly suitable for switchgear.
Prior art clamps of the kind including a clamp base portion and at least one clamp cover, a channel between the two parts formed by aligned grooves and a screw for connecting the parts together and thereby connecting two or more conductors have various disadvantages. Even at an amperage of only up to approximately 500 ampere two covers per clamp channel are required for connecting two aluminum cables or steel-aluminum cables, and with higher currents, the number of clamp covers is even larger. The clamps are therefore voluminous, heavy and expensive as regards material and costs. A plurality of clamp covers are required, mainly, because the attainable clamping force, and therewith the compression of the cables, are relatively low, even when screws are used which have a high tensile strength. Not more than a small portion of the current to be transmitted flows across the cover, because screws having a high tensile strength are poor conductors. For the current to be conducted substantially only by way of the bottom part of the clamp is also disadvantageous, insofar as it is desirable, on account of the skin effect that all strands of the outermost layer of the cable are contacted. However, this can be made possible by having the clamp base part of such a length that it can receive a length of cable which is at least half the pitch of the strands. Even when screws of an electrically highly conductive material are used and the conduction of the current by way of the cover would thus be improved, so that an almost uniform current loading of all wires of the outermost layer could be achieved, the clamps could not be of shorter dimensions because the clamping pressure attainable with such screws is relatively low, a fact which could only be compensated by the clamps being suitably lengthened.
A further disadvantage appears with conductors of a large cross-section. While the thermal play in the case of small cross-sections and the flow of aluminum in the case of aluminum cables can still be compensated by means of sets of springs, the clamping force of the screws being transmitted to the clamp body parts by way of these springs this solution cannot be applied to clamps for conductors of a large cross-section.
Also proved to be unsatisfactory were so-called transverse conduction plates, i.e., plates of an electrically highly conductive material, which plates envelop the conductor in the clamping channel like a jacket. These are used for the purpose of limiting the conductive connection between the clamping base part and the conductor, gripped in the clamp, to not only those wires or surface areas which project into the groove of the clamp base part. A substantial improvement of the contact conditions is obtained in this case but only at such clamping forces that cannot be obtained with conventional screws.
Compression screws are free from the aforementioned disadvantages. However, these clamps cannot be used, as a rule, when releasable clamps are required. Moreover, the pressure which must be applied by means of a press is very high, particularly when the clamp is large so that the handling of the press may cause difficulties on account of its size and mass.